Rotary cutting tool comprising two cutting portions having opposed cutting directions

ABSTRACT

A method of machining a workpiece with a rotary cutting tool extending along a longitudinal axis and including a first cutting portion including a plurality of first helical teeth having a helix direction and being designed to work in a first direction of rotation of the tool. The tool also includes a second cutting portion with a plurality of second helical teeth having, as helix direction, the same helix direction as the first cutting portion and being designed to work in a second direction of rotation of the tool, opposed to the first.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a divisional of U.S. application Ser. No.11/677,888 filed on Feb. 22, 2007, which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION AND DESCRIPTION OF THE PRIOR ART

The present invention generally relates to the field of rotary cuttingtools such as milling tools, also known as milling cutters.

The invention also concerns the field of machining methods using suchtools, in particular but not exclusively machining methods employed inthe area of aeronautical constructions. By way of indication, themethods in question may in particular be methods for producing parts ofengines intended to equip aircraft.

In the prior art, the machining methods aimed at obtaining such parts ofcomplex geometry often require the use of a multitude of successivemachining steps, and more specifically of a number of milling stepsduring which the tool used is moved with a circular cutting movementabout its own longitudinal axis, and the workpiece to be machined ismoved with any desired relative feed movement with respect to this tool.

In order to best optimize this type of method, it is known to a personskilled in the art to prefer a machining operation in “climb mode”rather than in “conventional mode”, these two modes being defined notonly as a function of the direction of rotation of the tool, itselfgoverned exclusively by the orientation of the helical cutting teethequipping this tool, but also as a function of the direction of therelative feed between this cutting tool and the workpiece to bemachined.

In light of the foregoing, it is clear that during the use of the methodfor machining a workpiece, when the direction of relative feed betweenthe cutting tool and the workpiece is imposed by the workpiece geometry,the fact of wishing to work with preference in the climb mode imposes adirection of rotation of the tool. That may therefore result in the needto employ a different tool from the one used in the preceding machiningstep whenever this previously used tool was designed to rotate in thedirection of rotation opposed to the new direction of rotation required.

This constraint of changing tools during the machining of one and thesame workpiece is clearly extremely penalizing in terms of productiontimes and costs, this disadvantage being of course all the moreconstraining when the number of separate machining steps to be carriedout is high.

Moreover, when the direction of relative feed between the cutting tooland the workpiece is not imposed and can thus be freely chosen by theoperator as a function of the direction of rotation of the tool and soas to allow working in climb mode, it may nevertheless occur that theoverall cutting force generated during this machining step does notresult in the workpiece being applied against the positioning restsconventionally provided on the machine but, on the contrary, in thissame workpiece being applied against clamping means which equip themachine and complement the positioning rests.

This latter configuration is clearly not desired in the sense that itdoes not allow good positioning of the workpiece to be maintained duringthe machining, this disadvantage being manifested by losses in terms ofcutting quality and precision.

Consequently, to allow working in climb mode and moreover generate anoverall cutting force resulting in the workpiece being applied againstthe positioning rests and not against the clamping means, it wouldprobably be required in this case too to have recourse to a change oftool in favour of a tool having an opposed direction of rotation.Nevertheless, that would involve being exposed to the aforementioneddisadvantages relating to the tool-changing operations.

SUMMARY OF THE INVENTION

The aim of the invention is therefore to provide a rotary cutting tooland a machining method which overcome the aforementioned problemsrelating to the embodiments of the prior art.

To this end, the subject of the invention is a rotary cutting toolextending along a longitudinal axis and comprising a first cuttingportion including a plurality of first helical teeth having a givenhelix direction and being designed to work in a first direction ofrotation of the tool. According to the invention, the tool additionallyincludes a second cutting portion offset from the first along thelongitudinal axis, this second cutting portion including a plurality ofsecond helical teeth having, as helix direction, the given helixdirection mentioned above, these second teeth being designed to work ina second direction of rotation of the tool, opposed to the first.

Thus, one of the special features of the present invention is that thecutting tool, preferably taking the form of a milling cutter, has twoseparate cutting portions, thereby allowing an overall reduction in thenumber of tool changes during the use of a machining method requiring amultitude of successive machining steps to be performed on one and thesame workpiece to be machined.

It is indicated first of all that when the direction of relative feedbetween the cutting tool and the workpiece is imposed by the workpiecegeometry, the fact of wishing to work with preference in climb modeimposes a direction of rotation of the tool to which the tool accordingto the invention can advantageously be adapted with ease. Specifically,when the new direction of rotation required is the same as in thepreceding machining step, the operation is then of course continued withthe cutting portion of the tool which has just been used, while in theopposite case where the new direction of rotation imposed is opposed tothat used in the previous machining step, all that is then required isto employ the other cutting portion of the tool to ensure that workingtakes place in climb mode during this new machining step.

This specific feature therefore makes it possible to considerably limitthe tool changes during a method of machining one and the same workpiecethat incorporates a multitude of machining steps, that resultingdirectly in significant savings in terms of production times and costs.

Moreover, it is noted that in the other cases where the direction ofrelative feed between the cutting tool and the workpiece is not imposedand can thus be freely chosen by the operator, this free choice can beadded to that of the direction of rotation of the tool offered by thetool according to the invention thanks to the twin presence of the twocutting portions. Thus, the operator advantageously has available twoparameters of which he can freely fix the combination in such a way asnot only to allow work to take place in climb mode but also to ensurethat the overall cutting force generated during the machining stepresults in the workpiece being applied against the positioning restsconventionally provided on the machine, and not against clamping meanswhich equip the machine and complement the positioning rests. As statedabove, the advantage associated with obtaining an application of theworkpiece against the positioning rests lies in the improvement in theretention of the workpiece during the machining, this advantage beingmanifested by increased cutting quality and precision.

Preferably, the given helix direction mentioned above is right-handed,this also being referred to as a “right-handed helix”. However, aleft-handed helix direction for the first and second helical cuttingteeth could be provided as an alternative, without departing from thescope of the invention.

Preferably, the first direction of rotation of the tool associated withthe first teeth is the clockwise direction in cross section as viewedfrom a sleeve of the tool toward the first cutting portion, thisdirection also being referred to as “right-cutting” direction. Moreover,the second direction of rotation of the tool associated with the secondteeth is the counterclockwise direction in cross section as viewed fromthe sleeve toward the second cutting portion, this direction for itspart also being referred to as “left-cutting” direction.

Preferably again, the first cutting portion is spaced apart from thesecond cutting portion along the longitudinal axis by a cylindricalintermediate portion of the tool, thereby facilitating its production.

Moreover, provision is preferably made for the first cutting portion tobe closer to a sleeve of the tool than is the second cutting portion.Nevertheless, the converse arrangement is also contemplated, withoutdeparting from the scope of the invention.

Finally, the cutting tool according to the invention is preferably amilling tool, namely a milling cutter intended to allow millingoperations during which the tool used is moved with a circular cuttingmovement about its own longitudinal axis, and the workpiece to bemachined is moved with any desired relative feed movement with respectto this tool, such as a substantially rectilinear or circular movement,for example.

Moreover, another subject of the invention is a method of machining aworkpiece using the rotary cutting tool which has just been set forthand which is mounted on a machine tool, the method comprising a firstmachining step using the first cutting portion of the tool and also asecond machining step using the second cutting portion of the tool,these first and second machining steps being carried out successivelywhile keeping the rotary cutting tool mounted on the machine tool.Therefore, the tool is advantageously not demounted from the machinetool between the two aforementioned machining steps, the only operationrequired between these two latter steps thus being a change of rotationof the tool.

Preferably, each of the first and second machining steps is implementedin such a way that the first and second cutting portions work in climbmode the material of the workpiece to be machined.

Preferably again, the first machining step is implemented in such a wayas to obtain a first direction of relative feed between the cutting tooland the workpiece to be machined, and the second machining step isimplemented in such a way as to obtain a second direction of relativefeed between the cutting tool and the workpiece to be machined, opposedto the first direction.

As mentioned above, the first and second machining steps are preferablymilling steps.

Other advantages and features of the invention will become apparent fromthe detailed nonlimiting description below.

BRIEF DESCRIPTION OF THE DRAWINGS

This description will be given with reference to the appended drawings,in which:

FIG. 1 represents a front view of a rotary cutting tool according to apreferred embodiment of the present invention;

FIG. 2 represents a view in cross section taken along line II-II of FIG.1;

FIG. 3 represents a view in cross section taken along line III-III ofFIG. 1;

FIGS. 4 and 5 schematically illustrate two successive steps of amachining method according to a preferred embodiment of the invention,implemented using the tool shown in FIGS. 1 to 3; and

FIG. 6 schematically illustrates a machining step implemented during amethod using the cutting tool shown in FIGS. 1 to 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference first of all to FIGS. 1 to 3, there can be seen a millingtool 1 according to a preferred embodiment of the present invention.

Overall, this tool 1 has, from top to bottom, a sleeve 2 designed formounting this tool on a suitable machine tool (not shown), a firstcutting portion 4, a cylindrical intermediate portion 6, and finally asecond cutting portion 8. Of course, all these elements are arrangedalong a longitudinal axis of the tool, referenced 10 in the figures,which also corresponds to an axis of rotation of this tool.

The first cutting portion 4 is equipped with a plurality of helicalcutting teeth 12, these teeth having a given helix direction, preferablychosen such that it is right-handed. By way of indication, it isrecalled that a “right-handed helix” is such that in two successivecross sections of the first cutting portion 4, starting from the sleeve2 toward the cutting end of the tool, the first teeth 12 are displacedin the clockwise direction. These first teeth 12 are designed to work ina first direction of rotation of the tool, which corresponds in crosssection as shown in FIG. 2 to the clockwise direction, when this sectionis viewed from the sleeve 2 toward this first cutting portion 4. By wayof indication, this clockwise direction is also referred to as“right-cutting” direction, and is represented schematically in this FIG.2 by the arrow referenced 14.

On the other hand, the second cutting portion 8 for its part is equippedwith second helical cutting teeth 16 provided with the same given helixdirection, that is to say a right-handed helix, while having a seconddirection of rotation opposed to the above-indicated first direction 14.Specifically, this second direction of rotation, shown schematically inFIG. 3 by the arrow 18, is such that in cross section viewed from thesleeve toward this second cutting portion 8, it corresponds to thecounterclockwise direction.

With reference now to FIGS. 4 and 5, these figures respectivelyschematically illustrate different steps of a machining method accordingto the present invention, this method being implemented using the tool 1which has just been set forth.

FIG. 4 shows a first step for machining a workpiece 20, this first stepbeing carried out using the first cutting portion 4, that is to say bycausing the tool 1 to rotate in the clockwise direction 14. In order towork in climb mode, the direction of the relative feed Vf between thetool 1 and the workpiece 20 is fixed as shown in FIG. 4, that is to sayby arranging for the workpiece 20 to move toward the right with respectto the tool 1 as viewed from above.

To conduct the second machining step shown schematically in FIG. 5, thetool is maintained in position on the machine tool (not shown), and thissame tool is caused to rotate in a direction opposed to that employedduring the first step schematically illustrated in FIG. 4. Therefore,this second step is implemented using the second cutting portion 8rotating in the counterclockwise direction 18. Moreover, again in orderto work in the preferred climb mode on account of the machining qualityprovided thereby, the direction of the relative feed Vf between the tool1 and the workpiece 20 to be machined is then reversed with respect tothat encountered during the first step, namely such that the workpiece20 now moves toward the left with respect to the tool 1 as viewed fromabove, as is shown in FIG. 5. In this respect, it is indicated that thisrelative feed between these two elements can be obtained by settingeither one of these two entities 1, 20 in motion, as is well known to aperson skilled in the art.

Thus, as was indicated above, it can be seen that when the direction ofthe relative feed Vf is imposed by the geometry of the workpiece 20 tobe machined, which geometry may moreover be relatively complex, all thatis then required is to choose that cutting portion of the two which willmake it possible, owing to the particular arrangement of the teeth whichit incorporates, to work in the preferred climb mode. In this respect,as is well known to a person skilled in the art, it is recalled that thedifference between the first helical teeth referred to as“right-cutting” teeth and the second helical teeth referred to as“left-cutting” teeth, these two sets of teeth moreover each being oneswith a right-handed helix, lies quite simply in the orientation of thecutting edge of these teeth.

The advantage resulting from the implementation of the method which hasjust been described thus consists in not having to demount the tool 1from the machine between the two successive machining steps.

With reference now to FIG. 6, this figure schematically illustrates theimplementation of a machining step carried out while performing adifferent process. This FIG. 6 shows the isostatic mounting that allowsthe workpiece 20 that is to be machined to be fastened to the machinetool, this mounting comprising as a whole a planar rest consisting ofthe three fixed rests 22, 24, 26, a rectilinear linear rest consistingof the two fixed rests 28, 30, a point rest consisting of the fixed rest32, and finally clamping means 34 that allow the workpiece to befastened and are as a whole situated opposite the aforementioned fixedrests.

This FIG. 6 shows that the direction of the relative feed Vf and alsothe cutting portion of the tool 1 have been jointly chosen in such a wayas not only to obtain working in climb mode but also as to obtain anoverall cutting force, referenced by the arrow Fc in FIG. 6, directedtoward the rests of the aforementioned isostatic mounting. That makes itpossible as a whole to obtain an application of the workpiece 20 againstthese same positioning rests provided on the machine, and not againstthe clamping means 34. This then results in an improvement in theretention of the workpiece during the machining, which is manifestedprimarily by increased cutting quality and precision. By way ofindication, it is noted that in the specific case represented in FIG. 6,it is the second cutting portion 8 which is used in such a way as toobtain left-cutting, that is to say so as to cause the tool 1 to rotatein the counterclockwise direction 18. On the other hand, the directionof the relative feed Vf between the tool 1 and the workpiece 20 to bemachined has at the same time been chosen such that this same workpiece20 moves toward the left with respect to the tool 1 as viewed fromabove, as is shown in FIG. 6.

Of course, various modifications may be made by a person skilled in theart to the invention which has just been described purely by way ofnonlimiting examples.

1. A method of machining a workpiece, said method comprising: providinga rotary cutting tool with a first cutting portion including a pluralityof first helical teeth having a helix direction, each of said firsthelical teeth having a first cutting edge oriented so as to cut in afirst direction of rotation of the rotary cutting tool, said rotarycutting tool further comprising a second cutting portion offset from thefirst cutting portion and including a plurality of second helical teethhaving said helix direction, such that said first and second helicalteeth have a same helix direction, each of said second helical teethhaving a second cutting edge oriented so as to cut in a second directionof rotation of the rotary cutting tool, wherein said second direction ofrotation is opposed to said first direction of rotation; mounting saidrotary cutting tool on a machine tool with a sleeve; performing a firstmachining step on said workpiece with said first cutting portion bycutting said workpiece with said first helical teeth along said firstdirection of rotation; and performing a second machining step on saidworkpiece with said second cutting portion of the rotary cutting tool bycutting said workpiece with said second helical teeth along said seconddirection of rotation, wherein said first and second machining steps areperformed successively while keeping said rotary cutting tool mounted onthe machine tool.
 2. The machining method as claimed in claim 1, whereineach of the first and second machining steps is implemented such thatthe first and second cutting portions work the workpiece in climb mode.3. The machining method as claimed in claim 1, wherein said firstmachining step is implemented in such a way as to obtain a firstdirection of relative feed between said rotary cutting tool and theworkpiece, and wherein said second machining step is implemented in sucha way as to obtain a second direction of relative feed between saidrotary cutting tool and the workpiece, opposed to said first direction.4. The machining method as claimed in claim 1, wherein said first andsecond machining steps are milling steps.
 5. The machining method asclaimed in claim 1, wherein said second cutting edge is orientedopposite the first cutting edge of said first helical teeth.
 6. Themachining method as claimed in claim 5, wherein said first direction ofrotation for said second helical teeth is clockwise and said firstdirection of rotation for said first helical teeth is counterclockwise.7. The machining method as claimed in claim 6, wherein said helixdirection is right handed.
 8. The machining method as claimed in claim1, wherein said mounting is performed so that said first cutting portionis closer to said sleeve than is said second cutting portion.
 9. Themachining method as claimed in claim 1, wherein said rotary cutting toolextends along a longitudinal axis, and said first and second helicalteeth have a same helical angle with respect to said longitudinal axis.10. The machining method as claimed in claim 1, wherein said workpieceis not demounted from said machine tool between said first and secondmachining steps and wherein the only step performed between said firstand second machining step is changing from said first direction ofrotation to said second direction of rotation.